This invention relates in general to vehicle wheels and in particular to two piece bimetal wheels having a wheel rim attached to a wheel disc with a bimetal transition insert.
It is known in the art to fabricate a vehicle wheel by attaching a wheel rim to a separately formed wheel disc. Typically, the wheel rim is rolled from steel strip stock and the wheel disc is stamped from steel sheet stock. The rim is welded to the disc to form the wheel. Such a wheel is shown in U.S. Pat. No. 5,257,455 to Iwatsuki. Alternately, the wheel rim can be rolled from steel and the wheel disc cast or forged from a light weight metal, such as aluminum, titanium or magnesium, or an alloy of a light weight metal. When the metals forming the wheel rim and wheel disc are different, it is difficult to provide a good weld between the rim and disc. To address this problem, a ferrous weld anchor is usually attached to the wheel disc. The wheel rim is welded to the weld anchor to assure that a good weld is formed between the rim and disc. Such a wheel is described in U.S. Pat. No. 3,506,311 to Nobach and is commonly referred to as a bimetal wheel. A bimetal wheel combines the economy, flexibility and strength of a steel rim with a pleasing aesthetic appearance of three dimensional contours formed in a cast or forged wheel disc.
To enhance the appearance of a two piece wheel, it is known to attach a full face wheel disc which includes the outboard tire retaining flange to a partial wheel rim to form a full face bimetal wheel. When a tire is mounted upon a full face wheel, the joint between the wheel disc and wheel rim is completely hidden and only the wheel disc is visible. A decorative finish is often applied to the face of the wheel disc to further enhance the appearance of the wheel. Examples of typical decorative finishes include metal plating, such as chromium plating, clear coatings and paint.
Referring now to the drawings, there is shown in FIG. 1 a fragmentary sectional view of a typical prior art bimetal full face wheel 10. The wheel 10 is described in the Nobach patent listed above and includes a full face wheel disc 12 formed from a light weight metal or light weight metal alloy by a conventional process, such as gravity, low pressure or die casting. The wheel disc 12 includes a central wheel hub 14 which is supported by a plurality of wheel spokes 16 (one is shown) within an annular sidewall 18. An outboard tire bead retaining flange 20 extends in a radial outward direction from the sidewall 18.
A ring-shaped weld anchor 22 formed from a ferrous material, such as steel, is partially embedded in the wheel disc sidewall 18. A portion of the weld anchor 22 is exposed to form a welding surface 24. The sidewall 18 further includes a cylindrically-shaped collar 26 which extends axially from the inboard side of the flange 20. The collar 26 extends radially over a portion of the weld anchor 22 to secure the weld anchor 22 to the wheel disc 12.
A conventional partial wheel rim 28 is attached to the inboard side of the wheel disc 12. The wheel rim 28 is formed from steel strip stock with conventional rim roll forming machinery. The wheel rim 28 includes an inboard end 30 which terminates in a conventional inboard tire bead retaining flange 32. An inboard tire bead seat 34 and inboard safety bead 36 are also formed on the inboard end 30 of the wheel rim 28. A leg portion 38 extends in an outward axial direction from the inboard safety bead 36. A deepwell 40 is formed in the wheel rim 28 adjacent to the leg portion 38. The wheel rim 28 also includes a cylindrically-shaped outboard end 42 which is adjacent to the deepwell 40. The outboard wheel rim end 42 includes an outboard tire bead seat 44 and outboard safety bead 46. The outboard rim end 42 extends over the wheel disc collar 26 and into contact with the welding surface 24 of the weld anchor 22. The outboard rim end 42 and the wheel disc collar 26 are sized to form a clearance fit therebetween, allowing the wheel rim 28 to be rotated relative to the wheel disc 12.
An alternate structure for the weld anchor is disclosed in U.S. Pat. No. 5,421,642 to Archibald where the weld anchor includes an annular collar which is received by the outboard end of a partial wheel rim. The weld anchor collar positions the wheel rim on the wheel disc.
A continuous circumferential air-tight weld 48 is formed between the wheel rim 28 and the weld anchor 22. Typically, a conventional friction or inertial welding process is used to form the weld 48. During the welding process, the wheel disc 12 is held stationary while the wheel rim 28 is rotated with the outboard rim end 42 pressed against the weld anchor 22. The heat generated by friction partially melts the outboard rim end 42 and the adjacent portion of the weld anchor 22 to form the weld 48.
While the wheel disc is typically welded to the wheel rim, it is also known to heat shrink the wheel rim onto the wheel disc, as shown in U.S. Pat. No. 4,363,347 to Baumgartner and European Patent Application No. 0 096 399 to Stahlschmidt & Malwurm GmbH & Co. KG. The U.S. Patent discloses wheel structures having either cylindrical or conical shrinkage surfaces. The U.S. Patent also discloses optional cutting or rolling of threads on the cylindrical shrinkage surfaces to allow the disc to be threadedly attached to the wheel rim.